CASHEW NUT PROCESSING In the world scenario, India occupies a premier position contributing about 43 per cent of the cashew nut production. Despite India being the largest producer and exporter of cashew nut, the production of raw cashew nut in the country is far below the requirement of the processing sector.
T
he cashew tree (Anacardium Occidentale L.) is evergreen (Fig.1). It grows up to 12 metres high and has a spread of 25 metres. Its extensive root system allows it to tolerate a wide range of moisture levels and soil types,
although,
production
commercial
is
advisable only in
well-drained,
sandy loam or red
soils.
Annual
rainfall needs to
be at least 889
mm (35 inches)
and
than
not
more
3048
mm
(120
inches).
Cashew trees are
most
frequently
found in coastal
areas.
Fig. 1. Cashew tree
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The main commercial product of the cashew tree is the nut. In the main producing areas of East Africa and India, 95 per cent or more of the apple crop is not eaten, as the taste is not popular. However, in some parts of South America and West Africa, local inhabitants regard the apple, rather than the nut kernel, as a delicacy. The origin of the cashew is Brazil, which is in the Latin American Zone. The cashew apple is used to manufacture jams, and soft and alcoholic drinks. In Goa, it is used to distil cashew liquor called “feni”. In the world scenario, India occupies a premier position contributing about 43 per cent of the cashew nut production. Despite India being the largest producer and exporter of cashew nut, the production of raw cashew nut in the country is far below the requirement of the processing sector. The maximum production of raw cashew nut was 5.2 lakh tonnes obtained from an area of 6.86 lakh ha during 1999-2000 (Fig.2). This production is hardly sufficient to meet 50 per cent of the demand of about 825 cashew-processing units in the country. The average demand growth rate for kernels for export and internal consumption is around 13 per cent per annum. The demand of the industry is about one million tonnes of raw cashew nut.
Fig. 2. Area and production of cashew nut in India (Source : http://agricoop.nic.in/hort/hortnew12 )
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Fig. 4. Cashew mango salad
Fig. 3. Salted cashew nuts
Uses of cashew nut kernel Cashew nut is the most versatile of all nuts. The kernels are low in carbohydrates but rich in proteins, fats and vitamins. The kernels are rich in nutrients and are put to use in a variety of ways. The kernels are used in cocktail parties and confectioneries. They are mostly salted (Fig. 3). The cashew nuts are also relished as salads by combining with mango (Fig. 4) and a variety of sweets can be prepared using cashew nut and a sweet named tikki (Fig. 5) and cashew cake (Fig.6) are of this unique kind.
Fig. 5. Cashew sweet (tikki)
Fig. 6. Cashew cake
The cashew nutshell liquid extracted from the hard shell is a by-product of the cashew industry. It is a versatile industrial raw material being used in preparation of resins, varnishes, paints, plastics, insecticides, brake linings, wood preservatives etc. The kernel oil is reported to be superior to olive oil and almond oil. The testa of the kernel is rich in tannins and hence mainly used in leather industry. It is also used as poultry feed. The brightly colored, swollen peduncle of cashew fruits is cashew apple (Fig. 7). The apple is fleshy, juicy and is rich in vitamin C.
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Fig. 7. Cashew fruits However, at present most of the produce is not at all utilized. From cashew apple, tasty drinks can be prepared mixing with juice of lime, pineapple, grapes, etc., Jam, chutney and pickles can also be prepared out of cashew apple. Liquor can also be prepared from cashew apple and it is termed as cashew wine (Fig. 8).
Processing of cashew nuts The various processes involved in the processing of cashew nuts are explained in detail as mentioned below. The process flowchart for the processing of cashew nut is shown in Figure 9.
Fig. 8. Cashew wine Cleaning All raw nuts carry foreign matter, consisting of sand, stones, dried apple etc. The presenceof foreign matter in the roasting operation canbe avoided by cleaning the nuts. The raw nutscan be sieved by handusing a ¾ inch mesh sieve. Soaking
The next stage is to soak the nuts in water to avoid scorching them during the roasting operation. This can be done by placing the nuts in a 40-45 gallon drum or vat and filling it with water until all the nuts are covered. After being left to stand for about ten minutes, the water should be drained off via a plug near the base of the drum. The nuts should then be left for periods of not less than four hours in order to allow the water left on the surface of the nuts to be absorbed. The process of covering the nuts with water, draining and standing should be repeated with the same nuts about three times until a moisture content of 9 per cent is reached. Where the production output runs from 2-10 tons of nuts per day, a simple cleaning and conditioning arrangement can be used. Two people open the sacks of harvested 4
nuts on a stand and clean the raw nuts as they are moved along a flat sieve, to two vats which are used for storage until the soaking process begins. Two vats are useful because one can be emptied while the other is being filled. Fig. 9. Process flow chart for processing of cashew nut
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Roasting
The application of heat to the nut releases the cashew nut shell liquid (CNSL) and makes the shell brittle which facilitates the extraction of the kernel when breaking the shell open. Three methods of roasting exist: open pan, drum roasting and the ‘hot oil’ method. The latter is more suitable to medium scale operations with Fig. 10. Cashew nut decorticator
associated higher equipment costs and viability of CNSL collection.
(i) Open pan
An open, mild steel, circular dished pan of around 2 feet in diameter is supported on a basic earth fireplace. When heated, 2-3 lbs (1kg) of nuts are placed on the pan at one time and stirred constantly. The CNSL starts to exude and then ignites. This produces a long flame and black smoke. After approximately two minutes, the pan is dowsed and the charred, swollen and brittle nuts are thrown out of the pan. The moisture evaporates quickly leaving the nuts ready for shelling. (ii) Drum roasting The idea of continually feeding the nuts into a rotating drum over a fire developed from the pan method. A slight horizontal slope in the mounting ensures the movement of the nuts through the drum. The drum is pierced so that the flames touch the nuts and the smoke is controlled by a hood and chimney arrangement. The nuts are dowsed using a continuous spray. This process was further modified by using the heat from the burning CNSL being harnessed to roast the nuts. The roaster consists of a contained helical screw, which moves the burning nuts at a controlled rate. The design was a distinct improvement, with little fuel being consumed and there being greater control on the roasting time. (iii) Hot oil method The principle employed in this method is that oil-bearing substances i.e. the shells, when immersed in the same oil at high temperature, will lose their oil, thus increasing the volume of the oil in the tank. For this method, conditioning becomes important. The equipment consists of a tank of CNSL heated to a temperature of 185- 190ºC by a furnace underneath and a wire basket used to hold the nuts for immersion into the tank. The depth of the basket must be sufficient so that the rim remains well above the oil during the roasting. Immersion time can range from 1½ to 4 min. About 50 per cent of the liquid is
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extracted from the nuts. Draining trays are needed at the end of the tank for the roasted nuts to dry and the residue oil can be returned to the tank. Caution must be taken not to heat the tank to over 200ºC because at this point polymerization of the CNSL takes place. The temperature can be maintained by continuous firing. The tank should be emptied and cleaned after each day’s roasting.
Shelling The objective of shelling is to produce clean, whole kernels free of cracks. In India, this operation has always been done manually. Other countries have difficulty in competing with the great skill and the low wages of the Indian workers. Therefore, India has enjoyed a virtual monopoly of cashew processing for a long time. Manual shelling is still relevant to the small-scale processor, although a close look at the mechanical option (Fig. 10) is advisable in all cases.
Manual shelling method In the manual shelling process (Fig. 11), the nuts are placed on a flat stone and cracked with a wooden mallet. As mentioned above, because of the residue CNSL, wood ash for covering the shells or gloves are required. An average sheller can open one nut in about six seconds or ten nuts per min. In an eight-hour working day, this amounts to about 4,800 nuts or about 5 kg of kernels.
Fig. 11. Manual shelling
At an extraction rate of 24 per cent, this quantity corresponds with about 21 kg of raw nuts per day or about 7 tons per year. However, experienced shellers in India can produce around half as much again, with a quality of 90 per cent whole kernels. Mechanical shelling method The most successful mechanical shellers work on nuts which have previously passed through the ‘hot oil’ process and is detailed under the paragraph ‘centrifugal shellers’. A semi-mechanised process that has been used predominantly in Brazil, uses a pair of knives, each shaped in the contour of half a nut. When the knives come together by means of a foot-operated lever, they cut through the shell all around the nut, leaving the kernel untouched. Two people work at each table; the first cuts the nuts and the second person opens them and separates the kernel from the shell. Daily production is about 15 kg
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of kernels per team. The first mechanised shelling system, Oltremare, is also based on two nut-shaped knives. The nuts are brought to the knives on a chain, each nut in the same position to fit between the knives. The nuts are pushed between the knives and cut. The chain itself has to be fed manually. After coming together, the knives make a twisting movement, thus separating the shell halves. The disadvantages of this method are that nuts smaller than 18 mm cannot be processed and output is reduced because not all the spaces on the chain can be filled which can count for as much as 10 per cent of the production volume. The shelling machines of the Cashco system are also chain fed but the nuts are automatically placed in the right position. The shelling device has two knives that cut the sides of the nut and a pin that is wedged into the stalk end of the nut separates the shell halves. The advantage of this system is a fully mechanised operation with an output of about 75 per cent whole kernel quality. Nuts smaller than 15mm cannot be processed. Centrifugal shellers use a system which is simple and enables a continuous flow. A rotary paddle projects the shells against the solid casing and the impact cracks open the shell without breaking the kernel. All sizes of nuts can be processed by this method, however, it is necessary to grade the nuts into four or so group ranges because a different rotary speed is used for the various size groups. The percentage of whole kernels produced is around 75 per cent. By preparing the shells with grooves and weakening the strength of them before the operation begins, the percentage can be increased. The speed of the rotor can thus be turned down and the risk of damaging the kernels is reduced.
Separation After shelling, shell pieces and kernels are separated and the unshelled nuts are returned to the shelling operation. Usually blowers and shakers are used to separate the lighter shell pieces from the kernels. The greatest problem is to recover small pieces of kernel sticking to the shell. This is usually done manually from a conveyor belt used to carry all the sorted semi shelled nuts. Pre-grading Pre-grading can be done before or after drying the kernels and may greatly reduce the final grading work. For large-scale processors pre-grading can be done mechanically, separating mainly the whole from the broken kernels and sometimes separating the different size groups of whole kernels.
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Drying The shelled kernel is covered with the testa and to facilitate removal, i.e. to peel in order to produce the blanched kernel, the shelled kernel is dried. This also protects the kernel from pest and fungus attack at this vulnerable stage. The moisture content is approximately 6 per cent before drying and 3 per cent after. It is important that the drying capacity is higher than the shelling capacity in case of periods of heavy rainfall because the drying operation will be lengthened since the kernels will absorb the moisture very quickly. Sun drying, Fig. 12. Mechanical drier
where the kernels are spread out in thin layers under
strong sunshine is possible, however artificial drying (Fig. 12) becomes necessary for medium or larger-scale producers. Drying usually takes six hours, at a temperature of around 70ºC. A uniform temperature throughout the drier is essential to avoid under drying or scorching. It is in the dried condition the kernels are most vulnerable, being both brittle (Fig. 13) and susceptible to insect infestation. Therefore, at this stage, they must be
handled with care and moved to the next stage of peeling as quickly as possible.
Fig. 13. Roasted Cashew nut wholes
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Peeling At this stage, the testa is loosely attached to the kernel, although a small amount of kernels may have already lost the testa during the previous operations. Gentle rubbing with the fingers does manual peeling. Those parts still attached to the kernel are removed by the use of a bamboo knife. One person can peel about 10-12 kg of kernels per day. The mechanised processes of peeling differ widely. They include air-blasting, suction, a freezing operation and a system of rubber rollers. The operation has a low efficiency due to the difficulty of removing the testa and the amount of breakages can be as high as 30 per cent. Currently research and development is taking place to improve the viability of the mechanisation of this operation.
Grading The grading operation is important, as it is the last opportunity for quality control on the kernels. With the exception of a few grading aids, all grading is done by hand. Power driven rotary sieves are one mechanical method, another being two outwardly rotating rubber rollers aligned at a diverging angle. For large operations looking towards export markets, it is necessary to grade the kernels to an international level.
Rehumidification Before the kernels are packed it is necessary to ensure that their moisture content rises from 3 per cent up to around 5 per cent. This is to make the kernels less fragile, thus lessening the risk of breakage during transport. In humid climates, the kernels may absorb enough moisture during peeling and grading to make a further rehumidification process unnecessary.
Packing The normal packaging for export of kernels is in air-tight tins of 25 lbs in weight. The packing needs to be impermeable as cashew kernels are subject to rancidity and go stale very quickly. The tin will be familiar to most tropical countries as it is a replica of the four gallon kerosene or paraffin oil tin. If possible the tins are made locally as movement of empty tins overseas is expensive. Alternatively, it might be arranged to purchase components and finish the manufacturing locally. This may be done by arrangement with tin manufacturers. The output of a tin manufacturing line is usually too large for one consumer but some cashew nut processors have in fact installed their own tin making plant and supply other processors. After filling and weighing, the cap should be soldered on in preparation for
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the ‘vita pack’ process. This consists of removing all air from the tin and substituting this with carbon dioxide (CO2). The advantages of packing cashew kernels in carbon dioxide are twofold. Firstly, carbon dioxide is an inert gas and will not support life. Any infestation that may have been present is, therefore, arrested. Secondly, carbon dioxide is soluble in cashew oil and goes into solution as soon as the seals are made. In a short space of time, it can be seen that a decrease in pressure takes place as the carbon dioxide goes into solution and the sides, top and bottom are drawn inwards. Thus the kernels are held tight in the tin, preventing movement and breakage during transport. Carbon dioxide, being a heavy gas causes the upward displacement of air and will remain in the tins after the filling process. Some large-scale machines will operate on six tins at a time, creating a vacuum in each and then filling with carbon dioxide. Some processors do not have vacuum pumps and displace the air in the tin by feeding in carbon dioxide through a small hole in the bottom of a side of the tin. The carbon dioxide valve is turned off when all the air has been replaced. The holes in the tin are then sealed, with the hole at the bottom of the side of the tin being done first, and the one on the top last.
Grades Cashew Kernels are graded into white/scorched wholes, pieces, splits (Fig. 14), butts etc., depending on the shape, size and colour of the kernel. The Government of India Act prescribes 33 different grades of cashew kernels. Only 26 grades are commercially available and exported.
Fig. 14. Cashew nut-splits
They are: W - 180,
is the ' King of Cashew ' - They are larger in size and very expensive.
W - 210,
is popularly known as 'Jumbo' nuts.
W - 240,
it is an attractive grade which is reasonably priced.
W - 320,
are the most popular among cashew kernels and highest in terms of availability, worldwide.
W - 450,
are the smallest and cheapest white whole kernels and hence the favorite among low priced whole grades.
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Scorched wholes are another grade of cashew kernels, which have a slight brown colour due to longer roasting. They have all the other characteristics of white kernels and have the same nutritional qualities. Butts, splits and pieces are priced lower and are ideal for cooking, preparation of sweets and savoury snacks.
# C.Indurani , # V.Jegadeeswari & # T.Arumuganathan Directorate of Extension Education, TNAU, Coimbatore – 3 Department of Food & Agriculture Process Engg, TNAU, Coimbatore – 3.
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